Multiband tunable system



Nov. 22, 1938. H. A. WHEELER MULTIBAND TUNABLE SYSTEM Original Filed May 28, 1931 INVENTOR. AROLD A. WHEELER.

ATTORNEY.

Patented Nov. 22, 1938.

Harold A. Wheeler, Great Neck, N. Y., assignor to Hazeltine Corporation, a. corporation of Delaware Original application May 28, 1931, Serial No.

540,581, now Patent No. 2,022,067, dated November 26, 1935. Divided and this application,

October 19, 1935,'Serlal No. 45,724

10 Claims. (Cl. 250-40) This invention relates to multi-band tunable over bands of. approximately equal frequenc systems and to methods of operating the same. coverage or width.

This application is a division of application The single figure of the drawing is a circuit Serial No. 540,581, filed May 28, 19 31 which isdiagram illustrating an embodiment oi the insued November 26, 1935, as Patent 2,022,067. vention as incorporated in the oscillator system a It is an object of this invention to provide a, which is pa ticu ar y applicable to radio st multi-band tunable system in which the scale eq p divisions on a tuning dial associated with the Referring now to the drawing, the 05011191501 tuning element of the system are relatively large Sy tem there S wn includes an arrangement to and easy to read accurately for each of two or Obta n 8- lm o V l tp when timed 0V6! more of the bands over which the s stem is tuna ar e ange 01' frequ n vTo enable the able. invention to be readily practiced, there are given The invention contemplates a multi-band tunum i a values for e elements, which have able system having a single variable tuning elebeen found satisfactory. 'ihese values are not ment for selectively tuning thes stem over any int d d to co titut limita ns upon-th w of the several bands, together with provisions ventionfor so varying the effectiveness of the tuning The system comprises three-electrode oscu element in accordance with the band selected latol tube Which y be O th W9 that the several bands are of approximately and l'esohant frequency-determining C cu t equal frequency coverage or width and equal 7 including a fixed inductance coil i8, a variable 29 changes in the resonant frequency of th system tuning condenser i4 and a number of fixed conare eiiected in two or mor of t bands by densers i6 and IT. The condensers it are adaptdisplacements of the tuning-element having ed to be connected in parallel with condenser nitudes in a ratio, from band to band in the and the condensers. in Series with order of decreasing frequency, which is substandense! by Switch as requiredone end 25 tially greater than the inverse ratio of the of coil is connected to the catmde of tube mean frequencies of the bands. This arrangeam! an intermediate Point of the con 13 'ment is to be distin h from the coupled to thegrid M of the tube through a tional multiband tunable system wherein the fixed grid condenser 26 (250 micro-microfarads).

an effectiveness of the tuning element remains The series combination of condenser i4 and one 39 I stant so that equal changes in the resonant frecondensers (one. of condensers w being quency of the system are eiTected in the several in Parallel with condenser is mnnecmd hands by displacements of the tuning element across the entire inductance having magnitudes in a ratio, from band to hand There 5 Provided feedback arrangement in th or of decrea i fr u which is which includes in a series circuit from the anode 35 equal to, or only slightly greater t the m to the cathode of the oscillator tube, the folverse ratio of the mean frequencies of the bands. lowing elements P order named: fixed In the particular embodiment of the invention densers 23 mlcrofarad) and micro hereinafter described in detail, the effectiveness microfamds), and an inductance which is ,40 0f the tuning element is varied in accordance ductively coupled to coil it. An inductance it 40 with the band selected so t t for all f the is connected between the intermediate point of bands substantially equal changes i t coil l8 and'the point between condensers 2i and onant frequency of the system are effected by The anode Potential is furnished by displacements of the tuning element that are y 25 (90 o necte b tween the oathof the same order of magnitude. ode and the anode through a choke coil it ('7 d5 Morespecifically, the invention contemplates mlllihehrl85)- e grid o the tube d a variable tuning condenser and an arrangement tively biased by a biasing battery 28 (about 20 by which one or more auxiliary normally fixed volts) which is connected between the cathode condensers are selectively connected in circuit and the grid of the tube t ou a h gridwith the variable condenser in accordance with leak resistance 21 (0.25 meBOhm 50 the band selected, the proportion and manner The out ut of t e oscillator s taken from of connection of the auxiliary condensers being ,across an output coil 20 which is coupled to insuch that the effective capacity of the combiductance l8. nation is adjusted for the several bands to cause The switch I! operates to connect condensers the system to be tuned by the variable condenser l6 and II in circuit, in pairs. Each pair of 55 series and parallel condensers enables the same tuning condenser H to cover a different frequency range. The variable condenser preferably has a capacity range of 42m 900 micro-microfarads. The following table gives the combinations of series and parallel condensers required to cover the given frequency ranges:-

Frequency Parallel Series conrange condenser denser Micro-micm- Micro-micro Kilocycles farada m operation of the switch it from the position decreased in successive steps as the system is corresponding to the lowest frequency band to the position corresponding to any of the other bands modifies the circuit relationship of tuning condenser l4 and inductance I8 by inserting one of the series condensers I! in circuit therewith, ,for, in such lowest frequency band, no series condenser is utilized.

It is also to be observed that the effectiveness of the tuning condenser is modified by the values of the series and parallel condensers connected in circuit therewith by the switch I5. The term effectiveness of a tuning element, as used herein, may be defined as the ratio of the maximum effective value of the circuit reactance of the same type as that of the tuning element to the minimum value thereof, as the tuning element is varied between its maximum and minimum values.

It is further apparent from the above table that the effectiveness of the tuning element is adjusted totune over successively higher frequency bands without increasing the magnitude of the effective capacitance in shunt with the inductanceelement ll. Thus, as the system is adjusted from the 500-700 kc; band to the 700-900 kc. band, the eflective capacitance, with the tuning condenser ll adjusted to its minimum value, is decreased from 626 micro-microfarads to 363 micro-microfarads; and, when the system is adjusted from the 700-900 kc. band to the 900-1100 kc. band, the effective minimum "capacitance is decreased from 363 micro-micro- I over these various ranges in frequency, the

condenser plates are made semi-circular but the axis of rotation is located eccentrically so that the radius of the entering edge of the rotor plates is one half the radius of the trailing edge.

Thus, with the that of coil 22.

This shape gives very nearly linear calibration over the intermediate-frequency range (900 to 1100 kilocycles) and only slight curvature in the frequency calibration of the other ranges.

The invention is described above as comprising an arrangement in which the effectiveness of the tuning element, or tuning reactance means, is modified so that for all of the bands equal changes in the resonant frequency of the system are effected by displacements of the tuning element that are of the same order of magnitude. It will be understood, however, that in certain applications it may be satisfactory to modify the effectiveness of this element to a lesser extent. Thus, in certain instances, a sufficient spread on the tuning indicator dial of the resonant frequencies in a higher frequency band may be obtained if the effectiveness of the tuning element in this band is considerably less than its effectiveness in the lowest frequency band. It will, therefore, be understood that the invention in its broadest aspects contemplates an arrangement, as described above, in which the effectiveness of the tuning element is varied in accordance with the band selected to effect, for two or more bands, equal changes in the resonant frequency of the system by displacements of the tuning elements having magnitudes in a ratio, from band to band in the order of decreasing frequency, which is substantially greater than the inverse ratio of the mean frequencies of the bands.

The combination of capacities described above has the advantage that a single half turn of the tuning condenser covers a frequency range of only one-fifth the. broadcast range, that all of the frequency, ranges are equal or at least of the same order of magnitude and that the scale divisions are relatively large and easy to read accurately and are approximately equal or of the same order of magnitude for all of the frequency ranges. Each of the five frequency ranges has an individually engraved scale on the condenser dial. The dissipation in the condensers and switching system is negligible, and the feedback is not varied when switching condensers, so that the output suffers no abrupt change with frequency at the boundaries between adjacent frequency ranges.

The feed-back coil i9 has a relatively low inductance and with incidental capacities has a .lower half of coil l8 are effectively included in this low-frequency resonant circuit but do not appreciably affect the resonant frequency because their combined inductance is much smaller than At high frequencies the reactance of coil 22 is so large that almost the entire radio-frequency plate current flows through condenser 2| and coil l9. a

By connecting the feed-back circuits so that coil I9 isv coupled to cell, l8 in a reverse direction, while coil 22 is connected to a tap on coil 18, the

feed-back current through condenser 2| and coil .IS has an effect which is augmented by the feedback current through coil 22 and the lower half of vcoll ll, the latter making a substantial contrlbution only at the lower frequencies. It is well known that an oscillator tuned by a variable condense; requires a greater amount of feedback at the lower frequencies than at the higher frequencies if the output is to be maintained at a uniform level over a frequency range. This result is accompiished with the circuit arrangement described above.

This circuit, is'utilized with excellent results as one element of a standard signal generator for testing radio receivers. The special tuning arrangement contributes greatly to the ease of opeter. Coll I9 is wound over the upper half of coil lid oration of this equipment.

. The coil structure is preferably constructed as iollows and located in a cylindrical copper can, 3.25" in diameter by 4.3' in length.

The coil l8 comprises 63 turns of No. 22 B. I; 3. gauge wire spaced 22 turns per inch on a cylindrical form 2" in diameter. proximately at the center. Feed-back coil is comprises 12 turns of No. 30 .B. 8; 8. gauge wire spaced 16 turns per inch on a cylindrical form 2%" in diameter. Output coil 20 comprises 50 turns of wire on a cylindrical form 1% in diamlt as indicated in the diagram, in order to prevent so-called parasitic oscillations" which otherwise occur at frequencies much higher than the resonant frequency of the oscillator system.

While I have described what I at present consider the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications, may be made therein without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications-as fall within the true spirit and scope of myinvention.

What is claimed is:

l. h multi-band tunable system comprising inductance means, capacitance means including a variable condenser connected in circuit with said inductance meansto form a circuit tunable over a given frequency band, auxiliary capacitance means, and switching means for modiiying the circuit relationship of said inductance and capacitance means and for including at least a portion of said auxiliary capacitance means in series with said capacitance means and at least a portion oi said inductance means to form a circuit tunable over a second frequency band and to modiiy in a predetermined manner the edectivenets of said variable condenser in tuning the latdill ter circuit, said auxiliary capacitance means being so proportioned, relative to the inductance means, the capacitance means and their circuit relation, that the. ratio of maximum to minimum edective capacitance oi the latter circuit is such that the system is tunable over a range of frequencies in the second hand which is of the same order of magnitude as the range of frequencies in the first band.

2. ii. multi-band tunable system comprising: a single inductance element and a plurality oi capacitance elements, at least one of said capacitance elements being variable; and switching means operable to one position to connect said inductance with a preselected group of said capacitance elements including a variable capacitance element to form a closed circuit tunable over a first frequency band and operable to a second position to connect said inductance element with another preselected group of said capacitance elements including a variable capacitance element to form a closed circuit tunable over a second banddiiiering from said first band.

and having an L/C ratio not substantially less than that of said first-mentioned tunable circuit, said groups of capacitance elements being so pro- The tap oif is apportioned that, for both of said bands, equal changes in the resonant frequency of said system are effected by displacements of said variable capacitance elements of the respective circuits that are of the same order of magnitude. 3. A variable tuning arrangement comprising in combination, a variable tuning condenser, two groups of auxiliary condensers, the auxiliary condensers of each group progressively differing in value in the same sense, and means for selectively connecting said variable condenser in series with a condenser of one group and in parallel with a corresponding condenser of the other group progressively to vary the effective capacitance of the arrangement and the effectiveness of said variable condenser.

4. A variable capacity arrangement comprising in combination a variable condenser, a plurality of series condensers, a plurality of parallel condensers, and a multi-point switch which at each position connects said variable condenser in series with one of said series condensers and in parallel with one of said parallel condensers said series and parallel condensers for each of said positions progressively varying in capacitance in the same sense, whereby the effective capacity of the combination is variable over a different range for each different position of said switch.

B. A resonant circuit comprising a variable condenser, a group of series and parallel condensers, and aseries-parallel switching arrangement connected with said condensers, said circuit being tunable over a set of contiguous frequency bands of approximately equal width, each diflerent band being selected by switching in a diilerent pair of said series and parallel condensers, and the fre- V quency variation within each at said bands being attested by said variablecondenser.

6. A variable tuning arrangement comprising in combination, a variable condenser, a plurality oi first condensers having progressively decreasing values, a plurality oi second condensers having progressively decreasing values, and switching means having a plurality of positions for selectively connecting, in successive positions thereof, said first condensers in parallel with said variable condenser and in their order oi decreasing value, and for selectively connecting, in said successive positions thereof alter its firstposition, said second condensers in series with said variable condenser and in their order of decreasing value, the several first and second condensers being so proportioned that the edectiveness of said variable condenser for the several positions of said switching means varies directly with the mean value oi the efiective capacitance of the arrangement.

7. h multi-band tunable system for operating over a plurality oi diflerent substantially mutu-' ally exclusive frequency bands comprising lined inductance means, a. variable tuning condenser, auxiliary capacitance means, and switch means operable to different positions, one for each of said bands, said switching means iorming in each of said positions a closed circuit tunable over one of said bands and including said variable condenser, and at least selected portions of said inductance means and said auxiliary capacitance means, said selected portions oi said auxiliary capacitance means being so proportioned, relative to said inductance means and said tuning condenser and their circuit relation, that for all of said bands e ual changes in the resonant frequency of said system are eflected by displacements of said variable condenser having magnitudes in a ratio, from band to band in the order of decreasing frequency, which is substantially greater than the inverse ratio of the mean frequencies of the bands.

8. A multi-band tunable system comprising fixed reactance means of a given type, variable reactance means of the opposite type connected in circuit with at least a portion of said firstnamed reactance means to form a circuit tunable over a given frequency range, auxiliary reactance means of said opposite type, and switching means for including said auxiliary reactance means in circuit with said tuning reactance means and at least a portion of said first-named reactance means to form a circuit tunable over a second band of higher mean frequency than said given band, said bands being substantially mutually exclusive, and to modify the effectiveness of said tuning means in tuning the circuit, said auxiliary reactance means being so proportioned relative to the first two reactance means and their circuit relation, that the L/C ratio of the circuit for said second band is not substantially less than the L/C ratio of the circuit for said given band.

9. A multi-band tunable system comprising fixed rea-ctance means of a given type, variable reactance meansof the opposite type connected in circuit with at least a portion of said first-named reactance means to form a circuit tunable over a given frequency range, auxiliary reactance means of said opposite type, and switching means for including said auxiliary reactance means in circuit with said tuning reactance means and at least a portion of said first-named reactance means to form a circuit tunable over a second band of higher mean frequency than said given band, said bands being substantially mutually exclusive, and to modify the effectiveness of said tuning means in tuning the circuit, said auxiliary reactance means being so proportioned, relative to the other reactance means and their circuit relation, that the L/ C ratio of the circuit for said second band is not substantially less than the L/C ratio of the circuit for said given band and a given change in the resonant frequency of said system when operating in said second band is effected by a displacement of said tuning element having a magnitude in a ratio to the magnitude of the displacement required to produce the same change in the resonant frequency of said system when operating in the lower frequency band, which is substantially greater than the ratio of the mean frequency of said given band to the resonant frequency of said second band.

10. A multi-band tunable system comprising, in combination, inductance means, variable capacitance tuning means connected in circuit with said inductance means to form a circuit tunable over a given frequency band, auxiliary capacitance means, and switching means for including at least a portion of said auxiliary capacitance means in series with said variable capacitance means and in circuit with at least a portion of said first means to form a circuit tunable over a frequency band higher than said given band and to modify the effectiveness of said variable capacitance means in tuning said latter circuit, said auxiliary capacitance means being so proportioned, relative to the first two means and their circuit relation, that a given change in the resonant frequency of said system when operating in said higher band is effected by a displacement of said tuning condenser having a magnitude in a ratio to the magnitude of the displacement required to produce the same change in the resonant frequency when operating in said given band, which is substantially greater than the ratio of the mean frequency of said given band to the mean frequency of said higher band.

HAROLD A. WHEELER. 

